1. Field of the Invention
The present invention relates to an electron emission device and more particularly, to a cold cathode which instantaneously emits high-density electrons depending upon applied electric field.
2. Description of the Related Art
Cathode ray tubes (CRTs) and so on which are generally used as display devices, use a thermionic cathode which is preheated to emit electrons therefrom. Alternatively, according to the recent development of electronics technology and semiconductor processing technology, cold cathode emission is under study, which lowers the work function of electron emission metal by an externally applied electric field and thus emits electrons instantaneously without preheating.
FIG. 1 illustrates a conventional cold cathode device. As illustrated, the conventional cold cathode includes a p-type substrate 11. A p+ region 12 is formed at the upper portion of the p-type substrate 11 and an n+ region 13 is formed at the neighborhood of the p+ region 12 and in the space formed from the p+ region 12.
Then, above the p+ region is formed an n++ shallow channel 14 which is connected with the n+ region 13, centered on the p+ region 12. The n++ shallow channel 14 contains a large amount of electrons by means of doping processes and so on. Above the n++ shallow channel 14 is located an anode 20 at a predetermined distance from the top of the n++shallow channel 14. The emitted electrons collide with the anode 20 and are absorbed therein.
The p-type substrate 11 which is made of crystalline bulk materials should be cut thin and trimmed, and if required, growing of an epitaxial layer having a good crystalline structure is preferred. Then, doping for adding impurities thereto, lithography, deposition and etching are repeated to form the p+ region 12, the n++ region 13 and the n+ +shallow channel 14 in sequence. The n++ shallow channel 14 is a region for enhancing an electron emission efficiency and is a channel which is less than or equal to about 300 xc3x85(that is, 10xe2x88x9210 m) in thickness in the form of a thin plate. Here, a symbol xe2x80x9c+xe2x80x9d in p+, n+, and n++ indicates impurity concentration contained in host materials.
In the above conventional electron emission device, a voltage VA is applied between the n+ region 13 and the anode 20 and a voltage VB is applied between the n+ region 13 and the p-type substrate 11. The voltage VA is applied to emit electrons from the surface of the n++ shallow channel 14 and is a high voltage of about 400-500 volts, which can be adjusted according to the features and degree of vacuum of the electron emission device, and the kind of the semiconductor material used in the fabrication. The voltage VB is applied to a pn junction formed by the p+ region 12 and the n++ shallow channel 14 and is a voltage of about 5-10 volts. As shown in FIG. 1, if the voltage VB is applied between the n+ region 13 and the p type substrate 11, the pn junction of the n++ shallow channel 14 and the p+ region 12 is reversely biased and an avalanche breakdown occurs in the n++ shallow channel 14. The avalanche breakdown means that a large number of electrons which are newly produced by successive collision of electrons due to an applied reverse bias in a highly doped host material contribute to electrical conduction. Thus-produced large number of electrons are accelerated to have energy exceeding the work function of the host material which is a material of the n++ shallow channel 14 and emitted in vacuum. Here, if the upper surface of the n++ shallow channel 14 is gilded with a material having a small work function, electrons are emitted although a forward bias voltage is applied between the p-type substrate 11 and the n+ region 13.
In the case of the above conventional cold cathode device, the upper surface of the n++ shallow channel 14 should be gilded with a material having a small work function such as cesium (Cs) in order to efficiently emit a large number of electrons, although the n++ shallow channel 14 for emitting electrons has been physically fabricated with the high doping state. However, since the above surface gilded material is evaporated together with the emitted electrons, it is difficult to maintain the initial surface gilded state. Moreover, a high degree of vacuum of about 10xe2x88x929-10xe2x88x9211 torr should be maintained between the n++ shallow channel 14 and the anode 20, which is also a very difficult matter to achieve.
Also, in the case of the above conventional cold cathode device, the area of the electron emitting portion is small in comparison to the whole area of the device, and thus the number of the emitted electrons is small and the use efficiency of the electron emission area is low. In this case, the electron emission area can be enlarged in fabrication. However, the electron emission area is increased, but the number of the emitted electrons not. Moreover, a surface processing and degree of vacuum is further required in order to increase the electron emission efficiency.
To solve the above problems, it is an object of the present invention to provide a cold cathode electron emission device activating electron emission by applying an external electric field, in which a single active region or a plurality of active regions are formed in the upper portion of a substrate, and high-density electrons are emitted by forming a shallow channel with an inversion layer electrically generated by the external electric field, and driving the shallow channel so that a Schottky effect and avalanche breakdown occur therein.
It is another object of the present invention to provide a cold cathode electron emission device activating electron emission by applying an external electric field, in which a shallow channel being an inversion layer is physically formed but is fabricated so that a number of active regions should be located below the shallow channel, to thereby emit high-density electrons by a number of active regions.
To accomplish the one object of the present invention, there is provided a cold cathode electron emission device activating electron emission by appliyng an external electric field, the cold cathode electron emission device comprising: a first type substrate which is a base of the electron emission device; at least one first type active region which is formed in the upper portion of the substrate and has a predetermined alignment pattern; a second type contact region which is formed in the upper portion of the substrate to surround the active region, around and spaced from the active region; and a gate region which is formed in the upper portion of the contact region at the state electrically insulated from the contact region, wherein a second type inversion layer is electrically formed on and around the upper portion of the active region by a voltage applied between the gate region and the substrate.
To accomplish the other object of the present invention, there is also provided a cold cathode electron emission device activating electron emission by appying an external electric field, the cold cathode electron emission device comprising: a first type substrate which is a base of the electron emission device; at least two first type active regions which are formed in the upper portion of the substrate; a second type contact region which is formed in the upper portion of the substrate to surround the active region, on and around and spaced from the active region; and a second type inversion layer connected with the contact region around the upper portion of the active region.